As shown in FIG. 1, a conventional motorboat 10 comprises a hull 11, an engine 12 mounted securely inside the hull 11, a water channel 13 which runs through the interior of the hull 11 to reach the rear end of the hull 11 from a water inlet 14 located at the bottom of the hull 11, a transmission shaft 15 having a front end capable of being driven by the engine 12 and having a rear end which extends to reach the inside of the channel 13, and a propeller 16 fastened to the rear end of the transmission shaft 15. The water is allowed to enter the water channel 13 via the water inlet 14. The water in the water channel 13 is acted on by the rotating propeller 16 driven by the engine 12 such that the water is forced out rapidly from the rear end of the water channel 13 to bring about a reaction force, which impels the motorboat 10 forward.
The water inlet 14 is generally provided with a guiding device 20 intended to prevent the water current in the water channel 13 from becoming turbulent. The turbulent water current in the water channel 13 can undermine the speed and the controllability of the motorboat 10.
The U.S. Pat. No. 3,757,728 discloses a guiding device of a platelike construction, which is provided with forked upper end extending into the water channel, and with a lower end extending to reach beyond the underside of the motorboat. Such a guiding device as described above is defective in design in that the forked upper end of the guiding device can cause easily the turbulent water currents, and that the speed of the motorboat is undermined by a resistance induced by the water current against the lower end of the guiding device, and further that the lower end of the guiding device is vulnerable to deformation caused by the impact of the water current, and still further that the lower end of the guiding device is a potential safety hazard to a motorboat operator or rider, as well as a swimmer.
The U.S. Pat. No. 4,237,812 discloses a frame-shaped grating, which is provided in the inner edge of the rear end portion thereof with a slope. Such a prior art grating as described above is rather ineffective in guiding the water current into the water channel of the motorboat and is not helpful in promoting the cruising speed of the motorboat.
The U.S. Pat. No. 5,114,368 discloses a water inlet grating comprising a vertical fixation plate which is provided respectively on both sides thereof with a guide piece extending outwards and horizontally. This prior art grating is defective in design in that the guide piece is susceptible to deformation caused by the impact of the water current in view of the fact that only side of the guide piece is fastened to the vertical fixation plate. In addition, the vertical fixation plate interferes the flow of the water current to bring about a turbulence at the time when the motorboat moves forward. Furthermore, the lower end of the fixation plate extends beyond the bottom of the motorboat and is therefore a potential safety hazard.
Such shortcomings of the prior art gratings as described above are overcome by a water inlet grating, which is disclosed in the U.S. Pat. No. 5,234,361. Nevertheless this water inlet grating has several deficiencies, which are described explicitly hereinafter.
The water inlet grating disclosed in the U.S. Pat. No. 5,234,361 is rather ineffective in guiding the water current to flow toward the portion over the water channel in view of the fact that the water inlet grating has only one guide piece which is obliquely disposed and is provided with the water current guiding surface having a recessed lower segment and a protruded upper segment. The guiding surface has an S-shaped side elevational view. As a result, when the water current passes the upper segment of the guiding surface, a forward pressure is brought about against the guide piece to undermine the forward momentum of the motorboat. Moreover, a motorboat is bound to move up and down in an undulating water. Such an up-and-down motion of the motorboat can cause a substantial reduction in the amount of water going into the water channel of the motorboat and can therefore cause a substantial amount of air to be sucked into the water channel of the motorboat to bring about the idling of the motorboat propeller.